Gas in mines is an ever-present hazard. An underground mine is an inhospitable place in which to work. Gas poisoning and explosion is a major hazard, with many different types of gas commonly present in mines. Black damp, a mixture of carbon dioxide and nitrogen, is formed because of corrosion and enclosed spaces so removing oxygen from the atmosphere and potentially causing suffocation. Fire damp hugely consists of methane, a highly flammable gas that explodes at concentrations between 5% and 15% or, if it does not explode, at 25% concentration it causes asphyxiation.
Methane ignition can trigger the much more dangerous coal dust explosion because the shock wave raises coal dust from the floor of the mine galleries to make an explosive mixture that is highly susceptible to spontaneous combustion.
Modern technology employed in mines, such as gas sensors, has dramatically improved safety. They respond to 28 common and exotic gases with excellent response linearity and high immunity to cross-contaminants. The gas sensors are approved to the demanding specifications issued by the mining industries in emerging regions and established markets.
Flammable and explosive gas sensors
In addition to being used in personal gas detection equipment, there are sensors, typically pellistors, used to detect combustible gases, which are installed in ruggedized gas detectors positioned on walls and machinery in mines. They are often installed on underground vehicles where they are subject to high levels of shock and vibration during normal operation, so for reliable operation pellistors must be mechanically robust as well as highly resistant to cross contamination from commonly occurring poison sources. The pellistor was originally developed as a far safer replacement for the flame safety lamp hitherto used as a flammable gas detector once battery lighting had replaced a naked flame as a source of illumination. The flame safety lamp was invented to replace the even more dangerous open candle flames previously used for illumination.